A variety of gastrointestinal tract disorders lead to bacterial overgrowth. Adequate evaluation and proper antibiotic therapy is required for this life-long illness. The current diagnostic test for bacterial overgrowth is a quantitative culture of small bowel fluid aspirate. There are many limitations to this technique including the invasiveness of intubations, exposure to X-rays for placing tubes in the intestine, high costs and poor diagnostic sensitivity of single aspirations. Our aim is to develop a diagnostic alternative to jejunal fluid analysis for the diagnosis of small bowel bacterial overgrowth. We propose to develop a safe diagnostic breath test which is non-radioactive, using xylose labeled with stable isotopes of carbon, 13C. The scientific foundation for the breath test is that the small bowel flora concentration can be estimated by the amount of bacterial 13C-xylose metabolism to 13CO2. The phase l research demonstrated the feasibility of using 13C-xylose to detect bacterial overgrowth. In phase Il, we intend to complete the development of the test into a reliable, cost-effective, diagnostic test. After establishing the test reliability, we will market a simple breath test kit for diagnosis of small bowel bacterial overgrowth.